Alkylate, as the term is used in the petroleum refining art, relates to a high octane product produced by the addition of an iso-paraffin, usually iso-butane, to one or more of the low molecular weight olefins, generally propylene or butylene, but also including amalene (pentene) or ethylene. The olefin source used to produce the alkylate is a biproduct of catalytic cracking. Generally, C.sub.3 and C.sub.4 olefins are produced in catalytic cracking. Isobutane is a product of hydrocracking processes.
Alkylation of isobutene with olefins was generally commercialized during World War II to provide a high octane component for aviation gasoline. It is now widely used as a source of high octane motor gasoline blending stock.
There are two major commercial alkylates processes, based on the acid catalyst used, HF or H.sub.2 SO.sub.4. Both types of processes can be operated to give essentially the same yield and octane alkylate using butylene and/or propylene feed with iso-butane. The primary differences in process design are based on reactor engineering, to accommodate process requirements of either type of process. The HF units normally operate at about 80.degree.-100.degree. F. and can be controlled with water cooling. H.sub.2 SO.sub.4 units require some form of refrigeration to control the temperature to below 50.degree. F. Other acid catalysts have been employed for alkylation. Ethylene alkylation using aluminum chloride catalysts produces a very high clear octane gasoline component. However, the costs for ethylene and aluminum chloride make this process less economical than the HF and/or H.sub.2 SO.sub.4 processes.
Isoparaffin-olefins alkylates, despite their high octane ratings, contain varying amounts of low octane components. Dimethylhexanes are prominent low octane components of those alkylates. The average RONs of the dimethylhexanes are well below 70, whereas, those of the trimethylpentanes are in the 100-110 RON range. The variance in the RON numbers for components of the alkylate are illustrated by the following table:
TABLE 1 ______________________________________ Components Contained in Isobutane HF Alkylates Component RON i-Butene.sup.a Butene-1.sup.a Butene-2.sup.a ______________________________________ 2,3-Dimethylbutane 103.5 1.5 0.6 2.5 vol % 2,3-Dimethylpentane 91.1 2.7 1.7 1.4 2,4-Dimethylpentane 83.1 2.3 1.3 2.4 2,2,4-Trimethylpentane 100.0 49.0 29.5 37.9 2,2,3-Trimethylpentane 109.6 1.5 0.9 2.4 2,3,4-Trimethylpentane 102.5 9.4 14.1 19.4 2,3,3-Trimethylpentane 106.0 6.8 8.2 10.1 2,4-Dimethylhexane 65.2 3.3 4.9 2.6 2,5-Dimethylhexane 55.2 2.9 1.9 2.8 2,3-Dimethylhexane 71.3 2.4 25.2 3.4 ______________________________________ .sup.a Olefin used to prepare isobutane alkylate